Composite pavement for highways, streets and airports with enriched limestone quarry waste as a coarse aggregate for the concrete of the subbase

ABSTRACT

Composite concrete pavement includes a surface course of normal concrete and a subbase or lower layer of concrete with coarse aggregate defined as enriched limestone waste of grading intermediate between coarse and fine aggregates. Coarse aggregate of this concrete is an enriched by-product of the manufacture of crushed limestone of regular sizes. As a raw material for enrichment, it should be finer than 9.5 mm. the amount of aggregate finer than 4.75 mm as a part of the total weight of aggregate should be not less than ½ before enrichment and close to, but not exceeding, ⅔ in the aggregate bin. Specified compressive strength and modulus of rupture of this concrete are up to 5,000 psi and 750 psi, respectively.

REFERENCE TO RELATED APPLICATION

Provisional Patent Application No. 60/446408

Filing Data Feb. 11, 2003

This Application is a Continuation-in-Part of patent application Ser. No. 10/775, 779, filed Feb. 10, 2004

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING PROGRAM

Not Applicable

BACKGROUND

1. Field of Invention

Present invention relates to the design and construction of highway, street, and airfield composite concrete pavements.

2. The Prior Art

Composite concrete pavements with surface course of normal concrete and subbase or lower layer of lean concrete are used widely in the US building practice to reduce the cost of pavement. The design procedure of Portland Cement Association Engineering Bulletin (Thickness Design for Concrete Highway and Street Pavements, Portland Cement Association, EB109P) indicates a thickness for two-layer concrete pavement equivalent to a given thickness of normal concrete. Lean concrete of modulus of rupture (MR) in the range from 150 to 450 psi for subbase and lower layer monolithic with normal concrete of surface course is taken for design charts of the composite pavement.

The design procedure of the normal concrete pavement results in a certain value of normal concrete thickness. The sense of composite pavements of the identical capacity is in the reduction of consumption of normal concrete with high cost crushed granite as a coarse aggregate by replacing of a part of this concrete by a subbase of cheaper concrete. The design procedure of composite concrete pavement should result in the equivalent normal concrete thickness of the same value as for the corresponding normal concrete pavement. The choice of flexural strength for subbase of composite concrete pavement is determined by merely economic reasons. An increase of flexural strength of concrete of the subbase means an increase of equivalent thickness of normal concrete pavement and a possibility of a corresponding reduction of thickness of normal concrete surface course of this pavement. Increase of equivalent normal concrete thickness of composite pavement due to an increase in flexural strength of the concrete of the subbase without changing of the thickness of subbase can be considered approximately as a measure of possible reduction of the thickness of the surface course of this pavement.

A design chart for composite concrete pavement with lean concrete subbase of modulus of rupture in the range from 150 to 450 psi is presented on the Fig.B1, Appendix 2 of said Portland Cement Association Engineering Bulletin. It an allows an estimation of the equivalent normal concrete thickness of a composite concrete pavement corresponding to the different combinations of thickness of lean concrete subbase and normal concrete surface course of pavement.

The values of equivalent normal concrete thickness of pavement corresponding to the lean concrete 4-inch thickness subbase of modulus of rupture in the range from 150 to 450 psi and values of thickness of surface course in the range from 7 to 10 inches were estimated according to this design chart. It allows an estimation of the change of equivalent thickness of composite pavement depending on the change of lean concrete flexural strength of subbase. Moreover, relative increase of this thickness depending on the increase of modulus of rupture of lean concrete of subbase were carried out, equivalent normal concrete thickness corresponding to the value of modulus of rupture equal to 150 psi being considered as 1,0. Results of these calculations are presented in Table 1. TABLE 1 Modulus of rupture of normal concrete of Modulus of rupture of normal concrete of surface course in the range 600 to 700 psi surface course in the range 500 to 600 psi Modulus of rupture of 4-inch thickness Modulus of rupture of 4-inch thickness lean lean concrete subbase, psi concrete subbase, psi 150 250 350 450 150 250 350 450 Thickness of Equivalent normal concrete thickness of composite pavement (inch) and relative normal concrete increase of this thickness depending on the increase of modulus of rupture of lean surface course concrete of subbase (equivalent normal concrete thickness corresponding to the value (inch) of modulus of rupture equal to 150 psi is considered as 1.0) 7 8.5/1.0  9.1/1.07  9.5/1.12 9.9/1.2 8.6/1.0  9.2/1.07 10.0/1.16 10.4/1.2  8 9.6/1.0 10.2/1.07 10.7/1.11 11.2/1.16 9.8/1.0 10.5/1.07 11.0/1.12 11.5/1.17 9 10.6/1.0  11.3/1.07 11.8/1.11 12.3/1.16 10.9/1.0  11.5/1.06 12.2/1.12 12.6/1.16 10 11.6/1.0  12.4/1.07 12.9/1.11 13.4/1.16 11.9/1.0  12.6/1.06 13.4/1.12 13.8/1.16

As can be seen from the Table 1, increase of equivalent normal concrete thickness of composite pavement due to increase of modulus of rupture of concrete of subbase from 150 to 450 psi constitutes at least 15%. It can be considered as an estimation of the corresponding reduction of the thickness of the normal concrete surface course.

Moreover, efficiency of composite pavement with lean concrete subbase can be estimated as a ration of equivalent normal concrete thickness of composite pavement to physical one (thickness of subbase plus thickness of surface course). Estimations of this ratio corresponding to the values of modulus of rupture of concrete in the range from 150 to 450 psi, the values of thickness of subbase equal to 4, 5, and 6 inches, and the values of normal concrete surface course in the range from 7 to 11 inches were calculated according to design chart Fig.B1 of said Engineering Bulletin. Average estimations of this ratio are presented in the Table 2. TABLE 2 Modulus of rupture of normal concrete of Modulus of rupture of normal concrete of surface course in the range 600 to 700 psi surface course in the range 500 to 600 psi Modulus of rupture of lean concrete of Modulus of rupture of lean concrete of subbase, psi subbase, psi Thickness of 150 250 350 450 150 250 350 450 lean concrete Ratio between equivalent normal concrete thickness of composite concrete pavement subbase in. and physical one of this pavement 4 0.803 0.856 0.902 0.936 0.829 0.877 0.923 0.962 5 0.786 0.835 0.897 0.912 0.810 0.858 0.906 0.950 6 0.707 0.819 0.864 0.864 0.793 0.840 0.895 0.944

It is evident that the efficiency of the use of lean concrete for composite concrete pavements increases with the reduction of the difference between the values of modulus of rupture of normal concrete of surface course and the lean concrete of subbase. The compressive and flexural strengths of lean concrete are determined to a great extent by the quality of the coarse aggregate. Lean concrete can be produced when local or recycled, relatively cheap coarse aggregates are available; the cost of concrete is determined to a large degree by the cost of coarse aggregate. The use of inexpensive small grains coarse aggregates is the one of the way of obtaining of lean and not only lean concrete. The name of Russian standard GOST 26633 is “Normal and small grains concrete”.

American building practice rejects the use of material finer than 9.5 mm and especially finer than 4.75 mm as a coarse aggregate, though the most popular sizes of coarse aggregate No.57 and No.67 according to ASTM C33 can include up to 15 and 10 percent of material finer than 9.5 mm and 4.75 mm, respectively. According to the Specification of Florida DOT (Section 346, Portland Cement Concrete), it is necessary to “produce all concrete using Size No. 57 or Size No. 67 coarse aggregate”. The nominal dimensions of these Sizes are in the range from 25.0 to 4.75 mm and from 19.0 to 4.75 mm, respectively. Grading of these sizes of coarse aggregate can include up to 15 and 10 percents of material finer than 9.5 mm and 4.75 mm, respectively. However these most popular in American building practice Sizes No. 57 and 67 of coarse aggregate for concrete are produced usually without content of material finer than 9.5 mm; material of grading (minus-⅜″) is considered as a primary fines, i. e. as by-product of manufacture of the coarse aggregates of grading required by consumer.

The stockpiling technology of limestone fines is presented in the report (2002) of the University of Florida “Research and Techno-Economical Evaluation: Uses of Limestone Byproducts”. According to said report “primary fines (minus-⅜ inch) originate during primary crushing and sizing/washing of aggregate raw material prior to processing by the commercial products plant. These material are commonly discarded as waste, while the plus-⅜″ material is further crushed and sized/washed to produce commercial coarse aggregate products. Byproduct fines produced during this latter stage of processing are termed secondary fines, and are either discarded as waste, or further processed into fines products. For the purpose of this study, two size fractions of both primary and secondary fines were examined, the coarse fraction (minus ⅜″ plus-200 mesh) including screening (minus-4 mesh, i. e. finer than 4.75mm, by plus -40 mesh), and the fine fraction (minus-200 mesh).”

According to the above report of Florida, “the accumulation of fines (minus-⅜ inch) produced by the coarse aggregate industry in the state of Florida is one of the major problems facing the industry today. According to a survey by the U.S. Bureau of Mines Mineral Industry, plant waste factors for all of the types of fines range from 15% to 25% of total production, a value likely underestimated for the coarse aggregate industry in the state of Florida. The survey also estimates that “there are presently 4 billion tons of quarry fines stockpiled in the United States. These quantities are likely to increase by another two billion tons by the turn of the century in response to increased production levels, stricter environmental regulations, and an increased demands for clean coarse aggregate products.” While discussing of this question nationwide, it should be taken into account that 70% of coarse aggregate in the U.S. building practice is crushed limestone, and about half of stockpiled limestone fines is screenings.

The cost of limestone screenings is half or less than crushed limestone of regular sizes and about one-fourth that of crushed granite of regular sizes ($3, 6-7, and 12-14 for short ton, respectively, as applied to Midwest and South). It relates to fresh by-product of manufacture of crushed limestone of regular sizes. As applied to stockpiled limestone fines, this difference should be considerably higher.

Objects and Advantages

The main object of the present invention is to obtain composite concrete pavement for highways, streets, and airfields with a surface course of concrete with hard rock as a coarse aggregate, thickness of the surface course being determined by requirements for abrasion resistance, and a subbase of concrete with the coarse aggregate defined as enriched limestone waste, the lower layer being monolithic with the surface course. Compressive and flexural strength of the concrete of the subbase of specified compressive strength and modulus of rupture up to 5,000 psi and more than 750 psi, respectively, can be at least close to that for concrete of the surface course. Concrete of the subbase requires a consumption of cement, which is less or at least close to that for concrete of a surface course of the same compressive strength with crushed granite as a coarse aggregate.

Another important object of the present invention is to obtain composite concrete pavement for highways, streets, and airfields with an asphalt surface course of thickness determined by requirements for the abrasion resistance, and a subbase of concrete of specified compressive strength and modulus of rupture up to 5,000 psi and more than 750 psi, respectively, with the coarse aggregate defined as enriched limestone waste. Capacity of this pavement is determined completely by the subbase of concrete with the coarse aggregate defined as enriched limestone waste. The asphalt cover layer reduces the temperature stresses and mitigates effects of distress factors in the joints between slabs

The most important object of present invention is to obtain concrete of specified compressive strength and modulus of rupture up to 5,000 psi and more than 750 psi, respectively, with a processed by-product of regular sizes crushed limestone manufacture defined as enriched limestone waste. Grading of this aggregate is intermediate between the least Size of coarse aggregates No. 89 and the largest Size of fine aggregates No.9 according to the ASTM C33. The compressive and flexural strength of concrete with this coarse aggregate should be higher or at least close to that for concrete of the same consumption of cement with crushed granite of regular sizes as a coarse aggregate. The amount of consumed cement for this concrete is at least close to that for concrete of the same compressive and flexural strength with crushed granite and crushed limestone of ordinary sizes as a coarse aggregate.

An important advantage of the present invention is the possibility of construction of a composite concrete pavement using very inexpensive concrete of compressive strength and modulus of rupture up to 5,000 psi and more than 750 psi, respectively, with enriched limestone waste as a coarse aggregate for the subbase of this pavement. Compressive and flexural strength of concrete for the subbase can be not less than that for the surface course of this pavement. As a result, equivalent normal concrete thickness of composite concrete pavement can be close to physical one of this pavement.

Another important advantage of the present invention is the opportunity to reduce the initial and especially the maintenance cost of composite concrete pavement by replacement of the surface course of concrete with hard rock coarse aggregate by an asphalt the surface course, thickness of surface course in all cases being determined by the requirements for abrasion resistance. The asphalt surface course reduces the temperature stresses and mitigates the effects of distress factors in the joints between slabs.

Yet another important advantage of the present invention is the possibility to use limestone quarry waste as a coarse aggregate of concrete instead of high-quality aggregate. It allows a very profitable utilization of great deposits of crushed limestone finer than 9.5 mm usually estimated as limestone quarry waste and especially aggregate finer than 4.75 mm. In so doing the volume of utilized aggregate finer than 4.75 mm should constitute about ⅔ of the volume of utilized aggregate finer than 9.5 mm. Utilization of limestone waste reduces quarrying of high-quality aggregate with a corresponding conservation of environment.

An additional important advantage of present invention is the possibility to carry out the mix design of concrete for concrete pavement based on the average compressive strength required according to ACI 318 since the close statistical connections between compressive and flexural strength of concrete allows an estimation of modulus of rupture of concrete depending on the specified compressive strength of this concrete. Utilization of this procedure provides a substantial reduction of the cost of concrete for concrete pavement construction.

SUMMARY OF INVENTION

The composite concrete pavement includes concrete with hard rock coarse aggregate or asphalt surface course of thickness determined by requirements for the abrasion resistance, and a subbase of concrete of specified compressive strength fc′ and modulus of rupture (MR) up to 5,000 and more than 750 psi, respectively. The coarse aggregate of concrete of the subbase defined as enriched limestone waste is of small grains crushed limestone of grading intermediate between the least Size of coarse aggregates No. 89 and the largest Size of fine aggregates No.9 according to the ASTM C33. This aggregate is a processed by-product of manufacture of crushed limestone of regular sizes. The limestone waste as a by-product of manufacture of crushed limestone of regular sizes is washed and clean material. The aim of enrichment of this by-product is the reduction of small sizes of grains. According to the invention the amount of material finer than 0.3 mm should not exceed about 3% of the total weight of coarse aggregate. This non-rigid limitation of the volume of grains of small sizes allows carrying out of enrichment of this aggregate by inexpensive sizing without more expensive washing.

Limestone quarry waste as a raw material for enrichment should be finer than 9.5 mm. The amount of aggregate finer than 4.75 mm (Sieve No.4) before enrichment should be about 50%. After enrichment the main part of aggregate finer than 4.75 mm should be coarser than 2.36 mm. The amount of aggregate finer than 2.36 mm (Sieve No. 8) after enrichment should not exceed about 10%; the amount of aggregate finer than 1.18 mm (Sieve No. 16) should not exceed about 7%; the amount of aggregate finer than 300 μm (Sieve No. 50) should not exceed about 2%.

The handling and transportation of enriched limestone waste from a quarry to the aggregate bin of a concrete plant causes an inevitable breakdown of aggregate. Due to weather effects and other impacts such as loading and discharge, grading of enriched limestone waste may become unpredictable. However, few parameters of grading of enriched limestone waste after transportation from a quarry to the aggregate bin of a concrete plant should be controlled in the framework of the present invention. The amount of aggregate finer than 4.75 mm (Sieve No.4) should be about ⅔ of the total weight of aggregate. The amount of aggregate finer than 300 μm (Sieve No. 50) should not exceed about 3.0%. Grading of enriched limestone waste after transportation from a quarry to the aggregate bin of a concrete plant can be considered as intermediate between the least Size of coarse aggregate No.89 and the largest Size of fine aggregate No.9 according to ASTM C 33.

The compressive and flexural strength of the concrete of the subbase with enriched limestone waste as a coarse aggregate can be not less than that for concrete of the surface course of this pavement. The amount of consumed cement for subbase is less or at least close to that for concrete of the same compressive strength with crushed granite of regular sizes as a coarse aggregate. As a result of the use of concrete with the different cost but with the same compressive and flexural strength for different parts of composite pavement, the equivalent normal concrete thickness of this pavement is close to the physical one.

Concrete of specified compressive strength and modulus of rupture up to 5,000 psi and more than 750 psi, respectively, with enriched limestone waste as coarse aggregate is very inexpensive and efficient. The use of this concrete for composite concrete pavement means a considerable reduction of the initial cost of construction this pavement and an increase of competitiveness as compared with asphalt pavement.

The use of concrete with this coarse aggregate allows very profitable utilization of great deposits of crushed limestone finer than 9.5 mm usually estimated as limestone quarry waste and especially aggregate finer than 4.75 mm. In so doing the volume of utilized aggregate finer than 4.75 mm should constitute about ⅔ of the utilized volume of aggregate finer than 9.5 mm. Utilization of limestone waste enables to reduce quarrying of high-quality aggregate with corresponding conservation of environment.

Moreover, a very considerable reduction of maintenance cost of this composite pavement can be achieved by the replacement of the surface course of concrete with hard rock coarse aggregate by an asphalt surface course, thickness of the surface course in all cases being determined by the requirements for abrasion resistance. Reduction of the temperature stresses and mitigation of effects of distress factors in the joints between slabs are achieved due to the effect of a thin asphalt surface course.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Composite concrete pavement includes a surface course of concrete with a hard rock coarse aggregate, the thickness of this surface course being determined by the requirements for abrasion resistance of the surface, and a subbase monolithic with the surface course. A processed by-product of the manufacture of crushed limestone of regular sizes defined conventionally as enriched limestone waste of grading intermediate between the least Size of coarse aggregate No.89 and the largest Size of fine aggregate No.9 according to ASTM C33 is used as a coarse aggregate for concrete of the subbase of this pavement. This concrete is characterized by the specified compressive strength f_(c)′ and modulus of rupture up to 5,000 psi and more than 750 psi, respectively. The consumption of cement for concrete with enriched limestone waste of this grading as a coarse aggregate is less or at least close to that for concrete of the same compressive and flexural strength with crushed granite of regular sizes as a coarse aggregate.

Portland Cement Association Engineering Bulletin (Thickness Design for Concrete Highway and Street Pavements, Portland Cement Association, EB109P) provides a thickness design of composite concrete pavement with lean concrete of the subbase of modulus of rupture in the range of 150-450 psi. The use of enriched limestone waste of grading intermediate between the least Size of coarse aggregate No.89 and the largest Size of fine aggregate No.9 according to ASTM C 33 as a coarse aggregate of concrete for subbase of the composite concrete pavement provides an increase in flexural strength of the subbase of the pavement. In spite of the differences of composition and cost of concrete for surface course and subbase their compressive and flexural strengths can be similar. In this case equivalent normal concrete thickness of this composite pavement determined according to said Engineering Bulletin is close to the physical one.

Enriched limestone waste is an inexpensive coarse aggregate, and it considerably determines the cost of concrete. The use of the concrete with this coarse aggregate allows a reduction in the initial cost of construction and should make concrete pavements more competitive as compared with asphalt pavements.

Operation of Preferred Embodiment

Portland Cement Association Engineering Bulletin (Thickness Design for Concrete Highway and Street Pavements, Portland Cement Association, EB109P) contains design charts for composite concrete pavement with subbase of lean concrete with the values of modulus of rupture in the range of 150-450 psi. This design procedure indicates a thickness for two-layer concrete pavement equivalent to a given thickness of normal concrete. The efficiency of the composite pavement can be estimated as a ratio of equivalent normal concrete thickness of pavement to the physical one of this pavement.

The Portland Cement Association Engineering Bulletin does not provide thickness design of composite concrete pavement with modulus of rupture of subbase higher than 450 psi. However modulus of rupture of concrete with enriched limestone quarry waste as a coarse aggregate for the subbase of composite pavement can exceed 450 psi. Moreover, it can be not less than that for the concrete with hard rock coarse aggregate of surface course of this pavement. In this case the equivalent normal concrete thickness of the composite pavement is equal to the physical one of this pavement, and the ratio of equivalent normal concrete thickness of pavement to the physical one is estimated as unity.

Equivalent normal concrete thickness of composite pavement with modulus of rupture of concrete for subbase intermediate between 450 psi and that for surface course can be estimated by the ratio of equivalent normal concrete thickness of this pavement to the its physical one. This ratio is in the range from that corresponding to the composite concrete pavement of value of modulus of rupture of concrete of subbase equal to 450 psi (Design charts Fig. B1 and B2 of said Engineering Bulletin) to unity. The ratio of equivalent normal concrete thickness to the its physical one for pavement of modulus of rupture of subbase, which is higher than 450 psi but less than modulus of rupture of surface course, should be estimated by interpolation.

For example, the equivalent normal concrete thickness of composite pavement of the 5-inches thickness subbase of concrete of modulus of rupture equal to 450 psi and 10-inches thickness normal concrete surface course of modulus of rupture equal to 700 psi can be estimated as 14 inches. The ratio of the equivalent normal concrete thickness to the physical one of this pavement (15 inches) is equal to 0.933. It is necessary to determine the equivalent normal concrete thickness of a composite concrete pavement of the same dimensions and the same flexural strength of the surface course but with the concrete of subbase of modulus of rupture equal to 600 psi. It should be estimated by the ratio of the equivalent normal concrete thickness of this pavement to its physical one. This ratio should be estimated by interpolation between that corresponding to the composite concrete pavements of the values of modulus of rupture of concrete of subbase or lower layer equal to 450 and 700 psi. This ratio can be estimated as 0.933+(1−0.933)*(600−450)/(700−450)=0.973, while the equivalent normal concrete thickness of pavement should be estimated as 15*0.973=14.6 inches.

The choice of the value of modulus of rupture of concrete of subbase and/or lower layer is determined by economic reasons.

Additional Embodiment

A composite concrete pavement includes an asphalt cover surface course of thickness determined by the requirements for abrasion resistance of the surface, and subbase of concrete of concrete of specified compressive strength fc′ and modulus of rupture (MR) up to 5,000 and more than 750 psi, respectively, the coarse aggregate of concrete of subbase defined as enriched limestone waste being the small grains crushed limestone of grading intermediate between the least Size of coarse aggregates No. 89 and the largest Size of fine aggregates according to the ASTM C33.

The capacity of said pavement is determined completely by the subbase of said concrete with the coarse aggregate defined as enriched limestone waste. The subbase of said concrete should be designed as a concrete pavement according to State Depatrment of Transportation or Agency road construction code. This technical decision of pavement allows a reduction of initial and maintenance cost of the pavement.

As applied to initial cost it means the replacement of concrete surface course by the less expensive asphalt. The asphalt surface course reduces temperature stresses in concrete of pavement. To reduce temperature stresses concrete of pavement aged 7-14 days is sawed into slabs. The existence of the asphalt cover layer reduces the difference between day and night temperatures and corresponding temperature stresses. It allows an increase in the dimensions of slabs and a corresponding reduction of sawing; sawing of concrete pavement is an expensive procedure. However the main effect of this type of structure relates to the maintenance cost of concrete pavement.

Maintenance cost of concrete pavement is determined by a bouquet of distress mechanisms considered in the Report of Pavement Research Center, Institute of Transportation Study, University of California at Berkeley, 2000, “Preliminary Evaluation of Proposed LLPRS Rigid Pavement Structures and Design Inputs”, p.p. 7-20 (extractions from this Report are included in the Appendix). These distress mechanisms include transverse joint faulting, pumping, corner cracking, transverse (fatigue) cracking with the considerable part of fatigue cracking being caused by edge effects, longitudinal cracking, and spalling of concrete at transverse joints.

The main part maintenance problems of concrete pavement are connected with joints between concrete slabs. The above Report of the University of California at Berkeley includes research of the main disteress factors of concrete pavements as applied to the California state network. It is based on the consideration of 520 parts of the road network of different length built between 1958 and 1974(Appendix A, p.p. 159-172 of said Report). Four of the main distress factors were considered:

Faulting at transverse joints occurred in 445 of considered parts of road of 520.

Only slight faulting was noticed in 102 considered parts of road of 520.

Moderate faulting and a somewhat uncomfortable ride occurred in 182 of considered parts of road of 520.

Severe faulting and a very uncomfortable ride quality occurred in 171of considered parts of road of 520.

Transverse fatigue cracking including fatigue cracking caused by edge effects which does not depend on the thickness of pavement, at least directly, occurred in 171of considered parts of road of 520.

Longitudinal cracking occurred in 79 of considered parts of road of 520.

Corner cracking occurred in 68of considered parts of road of 520.

Thus, a large part of the distress effects of concrete pavement, at least as applied to the California road network, are caused by off-design factors connected with the joints between slabs. In addition to a reduction of temperature stresses, an increase of dimensions of slabs and reduction of length of joints, the asphalt cover surface course mitigates the effect of these distress factors and reduces the maintenance cost of pavement.

Detailed Description of Yet Additional Embodiment

Concrete of the subbase of the composite concrete pavement is produced with the use of coarse aggregate defined as enriched limestone quarry waste of grading intermediate between the least Size of coarse aggregate No.89 and the largest Size of fine aggregate No.9 according to ASTM C 33. Physical properties of this coarse aggregate should be in accordance with requirements of the ASTM C33. This concrete is characterized by the specified compressive strength f_(c)′ and modulus of rupture (MR) up to 5,000 and more than 750 psi, respectively. Compressive strength of this concrete is higher at least by 10% than that for concrete of the same consumption of cement with crushed limestone of the least Size of coarse aggregate No.89 and the largest Size of fine aggregate No.9. Moreover, compressive strength of said concrete is substantially as high or higher than that of concrete of the same consumption of cement and twice as high consumption of admixture with crushed granite of regular sizes No. 57 and No. 67 of nominal dimensions 25.0 to 4.75 mm and 19 to 4.75 mm, respectively. Flexural strength of this concrete is higher than that for concrete of the same consumption of cement with crushed granite of regular sizes as a coarse aggregates.

Limestone quarry waste is a by-product of the manufacture of crushed limestone of regular sizes, mainly numbers 56, 57, 6 and 67 of the rated dimensions 25-9.5 mm, 25-4.75 mm, 19-9.5 mm and 19-4.75 mm, respectively. As a raw material for enrichment it should be finer ⅜ in.(9.5 mm). The proportion between the amounts of aggregate finer and coarser than 4.75 mm before enrichment is very important; the problem of utilization of aggregate finer than 4.75 mm is more urgent than that for the part of this by-product coarser than 4.75 mm. Moreover, aggregate finer than 4.75 mm is considerably cheaper than the part of this by-product coarser than 4.75 mm. According to the invention, the amount of aggregate finer than 4.75 mm at the quarry before enrichment should be about ⅓ of the total weight of aggregate.

Proportion between the amounts of aggregate finer and coarser than 4.75 mm before enrichment should be determined taking into account an inevitable breakdown of this aggregate due to dry enrichment by screening and especially due to transportation of this aggregate to a concrete plant. The breakdown of aggregate is caused by weather conditions (rain, frost, thawing) and handling of this aggregate (loading, discharge and other actions during transportation from quarry to aggregate bin of concrete plant). Due to the influence of scale effect this breakdown relates mainly to the portion of aggregate coarser than 4.75 mm. As a result, amount of aggregate finer than 4.75 mm in the aggregate bin of concrete plant can be considerably higher than at the quarry. The amount of this fraction in the aggregate bin of concrete plant should be about ⅔ of the total weight of aggregate. Transportation of the very vulnerable enriched limestone waste of 10 percent water-absorption from quarry to the concrete plant under adverse weather conditions results in the doubling the amount of aggregate finer than 4.75 mm-from ⅓ to ⅔ of the total amount of aggregate. Less water-absorption of aggregate and actual reduction of the quantity of adsorbed water means less breakdown of aggregate and more similar proportions between amounts of aggregate finer and coarser than 4.75 mm at the quarry and in the aggregate bin.

The aim of enrichment of limestone waste is a reduction of small size grains and to obtain the desirable proportion between the parts of aggregate. This by-product of manufacture of crushed limestone of regular sizes is washed and clean material. According to the invention the amount of material finer than 0.3 mm should not exceed about 3% of the total weight of aggregate. Enrichment of this by-product can be carried out by inexpensive sizing without more expensive washing.

Transportation of enriched limestone waste from quarry to the aggregate bin of concrete plant causes the reduction of amount of large size grains and a corresponding increase of the amount of small size grains since large size grains are more vulnerable. It can make grading of this aggregate variable and even unpredictable. However, a few parameters of grading of enriched limestone waste after transportation from a quarry to the aggregate bin of a concrete plant should be controlled in the framework of the present invention. The amount of aggregate finer than 4.75 mm (Sieve No.4) should be about ⅔ of the total weight of aggregate. The main part of aggregate finer than 4.75 mm should be coarser than 2.36 mm. The amount of aggregate finer than 300 μm (Sieve No. 50) should not exceed about 3.0%. Grading of enriched limestone waste as a whole after transportation can be considered borderline between coarse and fine aggregates in Terminology of ASTM C125, i. e. between grading of Sizes number 89 and 9 according to ASTM C33.

According to the definition of ASTM C 125 (Standard Terminology Relating to Concrete and Concrete Aggregates) “coarse aggregate, n-(1) aggregate predominantly retained on the 4.75-mm (No.4) sieve; or (2) that portion of an aggregate remained on the 4.75-mm (No.4) sieve”. As applied to the enriched limestone waste as a coarse aggregate of claimed concrete in aggregate bin of concrete plant the amount of aggregate finer than 4.75 mm (Sieve No.4) should be about ⅔ of the total weight of aggregate. The increase in the part of material finer than 4.75 mm up to about ⅔ of the total weight of the aggregate means a very efficient way of utilization of great deposits of limestone fines.

Experimental investigations of the washed by-product of manufacture of crushed limestone as a coarse aggregate for concrete were carried out in Moscow Institute of Concrete and Reinforced Concrete (NIIZHB). These investigations were necessary due to the shortage and high cost of crushed granite as a coarse aggregate in the Moscow region; it was an attempt to find less expensive coarse aggregate at least for concrete of middle strength. Enriched limestone waste product of Lavsk quarry of Lipetsk region (350 km South East of Moscow) was used for this purpose. This is the washed by-product of the manufacture of crushed limestone of regular Russian Sizes 5-20 mm (the closest American Size is number 67, 19-4.75 mm) and 20-40 mm defined as Russian fraction 3-10 mm.

Samples were taken from a large volume cone according to the Russian standard (very close to the similar ASTM standard) and were delivered to Institute laboratory in bags retaining quarry grading after enrichment of this aggregate. The crushing strength of limestone waste was estimated by compressing in a 150 mm-diameter cylinder. Loss of weight of tested samples made up 17%. According to the Russian building code, this loss of weight corresponds to compressive strength of coarse aggregate equal to 600 kgf/cm² (near 8500 psi). This is half as much as minimum strength of crushed granite Grades 1200-1400 kgf/cm².

Water-absorption of limestone waste is equal to 10%; specific gravity is equal to 2.46 g/cm³; bulk density is equal to 1390 kg/m³; the voids volume is estimated as 43%.

Frost resistance of limestone waste was determined by the test of samples in the solution of sodium sulfate with subsequent drying. The loss of mass after 10 cycles made up 10%. According to the Russian building code, frost resistance of limestone waste is estimated as Grade F50. The content of dissoluble silica in limestone waste makes up 21 milliliters per liter.

Samples of aggregate were dried to constant weight. Averaged results of sieve analysis of enriched limestone waste as a coarse aggregate defined as fraction 3-10 mm according to the Russian building code are presented in Table 3 in the form adopted in the US building practice. TABLE 3 Dimensions of Square Openings (mm) Less 12.50 10.00 5.00 2.50 than 2.5 Sieve residue (%) 0.75 0.75 64.00 25.50 9.0 Amount finer than each 99.25 98.5 34.50 9.00 — laboratory sieve (%)

As can be seen from Table 3, grading of this aggregate considered as a quarry grading is close to that for Size number 89 as the least Size of coarse aggregate according to ASTM C 33. A sample of washed finer limestone waste from a neighboring quarry defined as a 2-5 mm Russian fraction of fine aggregate of grading close to that for the largest Size of fine aggregate number 9 according to ASTM C 33 also was tested as a coarse aggregate of concrete. Physical properties of aggregates fractions 3-10 and 2-5 are the same. It was made for an estimation of the change of concrete strength depending on the change of grading of small grains crushed limestone used as a coarse aggregate of this concrete. Moreover, comparison of concrete strength of samples with coarse aggregate of the different grading allows estimation of the change of strengths of concrete caused by a possible breakdown of this aggregate due to handling and transportation from quarry to aggregate bin of concrete plant. Results of sieve analysis of this aggregate (Russian fraction 2-5 mm) are presented in Table 4. TABLE 4 Dimensions of Square Openings(mm) 5.0 2.5 1.25 0.63 0.315 0.16 under 0.16 Sieve residue (%) 20.5 69.5 8.75 0.45 — — 0.8 Amount finer than each 79.50 10.00 1.25 0.8 0.8 0.8 laboratory sieve (%)

To estimate compressive strength of concrete with washed limestone waste of fractions 3-10 and 2-5 mm as a coarse aggregate standard cubes 10×10×10 cm were made with the use of Portland cement Brand 500-DO-N of the Oscol cement plant without admixture. According to the Russian building practice of production of precast concrete cubes were subjected to standard steam-curing according to following pattern; 3+3+6+4, i.e. 3 hrs of conditioning, 3 hrs of the temperature rise 80° C., 6 hrs of isothermal warming, and 4 hrs of cooling. One-day compressive strength of steam-cured concrete makes up 60-65% of 28-day strength of this concrete. 28-day compressive strength of steam-cured concrete makes up 90% of 28-day strength of concrete of natural maturing. Test results of compressive strength of concrete brought to the standard European cube 15×15×15 cm and corresponding estimations of cylindrical strength (psi) are presented in Table 5. Cylindrical strength of concrete is estimated to be 1.2 times less than the cubic strength of this concrete. Concrete mixes number 1, 3, 5 were made with enriched waste defined as a Russian fraction 3-10 mm (Table 3) as a coarse aggregate, mixes number 2, 4, 6 were made with an aggregate defined as a Russian fraction 2-5 mm (Table 4) as a coarse aggregate.

As one can see from Table 5, the use of crushed limestone of Russian fraction 3-10 mm with the grading close to that for Size No.89 as a coarse aggregate for concrete allows to achieve compressive strength of concrete in the range from 1,000 to 5,000 psi. Finer crushed limestone of Russian fraction 2-5 mm of grading close to that for the Size number 9 is less efficient as a coarse aggregate. Compressive strength of concrete with this coarse aggregate is less at least by 10% than that for concrete with coarse aggregate of grading close to that for the Size number 89. TABLE 5 Composition of ready-mixed Cubic compressive Concrete (kg/m{circumflex over ( )}3) strength Mpa/ Water/ Density of Cylindrical compressive Coarse cement mix Slump strength psi Number Cement Sand aggregate ratio (kg/m{circumflex over ( )}3) (cm) 1 day 28 days 1 198 751 1,068 1.05 2,225 6.5 5.8/690  10.0/1190  2 197 740 1,066 1.05 2,210 7.0 4.8/570  8.0/950  3 347 596 1,091 0.61 2,245 8.0 19.4/2,310 29.0/3,450 4 350 580 1,100 0.60 2,240 8.5 17.9/2,130 28.3/3,370 5 498 478 1,075 0.43 2,265 7.5 37.1/4,420 42.0/5,000 6 500 483 1,060 0.42 2,255 9.0 31.1/3,700 38.4/4,570

All said above relates to concrete with coarse aggregate of washed limestone waste delivered to the Institute laboratory from the quarry without a change of its grading. It is necessary to estimate the actual breakdown of this aggregate due to transportation from quarry to plant and its impact on the concrete strength. The efficiency of the use of enriched limestone waste as a coarse aggregate in industrial conditions was checked at the Moscow plant of precast concrete No.10. Crushed limestone of the grading of Russian fraction 3-10 with water-absorption equal to 10% as a very vulnerable coarse aggregate was used for this aim. Ten double-side tipping wagons with 500 m³ of enriched limestone waste were delivered from the Lavsk quarry to the concrete plant. Grading of this aggregate at the quarry is presented in Table 3. Results of sieve analysis of this limestone waste at the concrete plant are presented in the Table 6. TABLE 6 Dimensions of Square Openings(mm) 10.0 5.0 2.5 1.25 0.63 0.315 0.16 Under 0.16 Sieve residue (%) 2.4 30.6 58.7 3.0 0.9 1.66 2.2 0.54 Amount finer than each 2.4 67.0 8.3 5.3 4.4 2.74 0.54 — laboratory sieve (%)

As can be seen from the Table 6, grading of enriched limestone waste at the concrete plant considerably differs from the grading of this aggregate at the quarry after enrichment. It changes due to loading, autumn rains, and moving by bulldozers to aggregate bin after discharge from wagons on concrete pavement of the concrete plant store. The amount of aggregate finer than 5 mm constituted near ⅓ of the total weight of aggregate before transportation to the concrete plant, while the amount of this aggregate at the concrete plant is close to the ⅔ of the total weight of aggregate. The main part of aggregate is finer than 5 mm and coarser than 2.5 mm. Grading of enriched limestone waste after transportation to the concrete plant can be considered close to intermediate between coarse and fine aggregates in Terminology of ASTM C125, i. e. between grading of Sizes number 89 and 9 according to ASTM C33.

The tests of concrete with limestone waste of this grading were carried out, the consumption of cement being the same as for prestressed piles. It was made to estimate maximum compressive strength of concrete with crushed limestone as a coarse aggregate of this grading. Concrete for piles is produced only with granite crushed stone as a coarse aggregate, and consumption of portland cement Brand 500-DO-N of the Volsk cement plant for this concrete is equal to 460 kg per cubic meter of concrete. The peculiarity of concrete for prestressed piles is the required one-day cubic compressive strength, which should be not less than 30 Mpa. This cubic strength corresponds to a cylindrical strength equal to 3570 psi. According to the Russian building practice of producing of precast concrete, cubes were subjected to the standard steam-curing according to next pattern; 3+3+6+4, i.e. 3 hrs of conditioning, 3 hrs of the temperature rise to 80° C., 6 h warming, and 4 hrs of cooling. Test results of concrete are presented at the Table 7. TABLE 7 Cubic compressive strength Composition of ready-mixed Mpa concrete (kg/m{circumflex over ( )}3) Cylindrical compressive strength Water/ psi Coarse cement Admixture Slump 1 day 28 days Number Cement Sand aggregate ratio (%) (cm) f cu f cu avg f cu f cu avg 1 500 483 1060 0.324 — 6 20.9 22.60 29.9 30.60 24.3 2,960 33.3 3,640 2 500 483 1060 0.308 0.5 7 21.8 21.10 30.4 29.45 20.5 2,510 28.5 3,505 3 500 483 1060 0.420 — 8 20.9 20.65 39.9 39.45 20.4 2,460 39.4 4,700 4 500 512 1110 0.370 — 6 23.8 24.50 46.5 46.05 25.2 2,920 45.6 5,480 5 500 512 1110 0.280 0.3 6 41.8 42.00 46.1 47.75 42.2 5,000 49.4 5,685 6 450 560 1110 0.280 0.3 6 35.6 34.80 40.9 40.40 33.7 4140 39.9 4,810 7 400 610 1110 0.280 0.3 4 32.3 34.20 43.2 43.45 36.1 4070 43.7 5,170

Three first series of tests can be considered as attempts of fitting to very unusual coarse aggregate; crushed limestone was not used as a coarse aggregate on the plant. Four other series of test of this concrete should be considered as quite successful. Enriched limestone waste as a coarse aggregate after considerable breakdown caused by the handling and transportation to the concrete plant in the adverse weather conditions allows to obtain concrete of specified compressive strength up to 5,000 psi and even more.

The efficiency of enriched limestone waste of the certain grading as a coarse aggregate can be estimated by the compressive strength of concrete with this coarse aggregate. As can be seen from the Tables 5 and 7, enriched limestone waste of grading intermediate between the coarse and fine aggregate in the Terminology ASTM C125 is more efficient as a coarse aggregate than crushed limestone of grading close to that for the Size No.89 and grading close to that for the Size No.9 according to the ASTM C33. Compressive strength of concrete with crushed limestone of this grading as a coarse aggregate is higher at least by 10% than that for concrete of the same consumption of cement with crushed limestone of grading close to that for the Size No.89 as a coarse aggregate. The compressive strength of this concrete is considerably higher than that for concrete of the same consumption of cement with crushed limestone of grading close to that for the Size No.9 as a coarse aggregate. Moreover, consumption of cement for concrete with crushed limestone as a coarse aggregate of grading intermediate between the coarse and fine aggregate in Terminology ASTM C125 is less at least by 10% than that for concrete of the same compressive strength with crushed granite of regular sizes as a coarse aggregate. One-day concrete strength exceeding the required for prestressed piles was achieved with a reduction in the consumption of cement by more than ten-percent and half as the consumption of admixture as compared with that for concrete with crushed granite as a coarse aggregate (Tables 5 and 7).

Thus, crushed limestone of the amount of aggregate finer than 4.75 mm about ⅔ of the total weight of aggregate, of the amount of aggregate finer than 4.75 mm but coarser than 2.36 mm in the range 55-60% of the total weight of aggregate, of the amount of aggregate finer than 0.3 mm not exceeding about 3% of the total weight of aggregate can be considered as a coarse aggregate of optimal grading in terms of compressive strength of concrete. This grading can be considered as intermediate between the coarse and fine aggregate in the Terminology ASTM C125. Concrete with crushed limestone of this grading as a coarse aggregate requires less consumption of cement and admixture than concrete of the same compressive strength with crushed granite and any hard rock aggregate of regular sizes as a coarse aggregates. Concrete with crushed limestone of this grading as a coarse aggregate requires less consumption of cement than concrete of the same compressive strength with crushed limestone of grading corresponding to that for Sizes number 89 and 9 according to ASTM C33 as a coarse aggregate.

Variation of grading of enriched limestone waste is inevitable; it is in the nature of this material. Requirements for grading of enriched limestone waste as a coarse aggregate at the quarry after enrichment and in the aggregate bin of concrete plant should limit influence of variation of grading of this aggregate on the strength of concrete. However, adverse conditions of transportation of this aggregate to the concrete plant can cause its excessive breakdown. It does not mean that enriched limestone waste of this grading can not be used as a coarse aggregate for concrete. However excessive breakdown of this coarse aggregate influences the strength of concrete. If the amount of aggregate finer than 4.75 mm exceeds ⅔ of the total weight of aggregate in the aggregate bin, it means reduction of concrete strength. Additional consumption of cement is required for compensation of degradation of this aggregate.

Tests of concrete with the different grading of crushed limestone as a coarse aggregate allow estimation of the acceptable limits of variation of grading of enriched limestone waste as a coarse aggregate in aggregate bin of concrete plant. As can be seen from the Tables 5 and 7, compressive strength of concrete with crushed limestone of grading close to that for the Size No.9 is less at least by 10% than that for concrete with crushed limestone of grading close to that for the Size No.89. Compressive strength of this concrete is considerably less that for concrete with crushed limestone of grading intermediate between the coarse and fine aggregate in the Terminology ASTM C125. The use of enriched limestone waste of grading finer than that for the Size number 9 as a coarse aggregate should be considered as undesirable; the additional breakdown of aggregate requires non-proportional an increase of consumption of cement.

Flexural strength of concrete is an important quality of concrete. As applied to the thickness design of concrete pavement, flexural strength is the main quality of concrete. Concrete with crushed limestone as a coarse aggregate of grading intermediate between the coarse and fine aggregates in the Terminology ASTM C125 can be considered as optimal in terms of flexural strength at least as compared with concrete with hard rock coarse aggregates of regular sizes. Compressive strength of concrete with this coarse aggregate is higher than that for concrete of the same consumption of cement with crushed granite of regular sizes as a coarse aggregate, and the increase of compressive strength of concrete means an increase of flexural strength of this concrete.

As with the strength of any structural material, the flexural strength of concrete should be characterized by the specified value, design flexural strength being estimated as a part of specified flexural strength. American building code ACI 318 and documents of Portland Cement Association do not contain a definition of specified concrete flexural strength. Current of thickness design procedure of concrete pavements allows considering the modulus of rupture (MR) as a specified concrete flexural strength. According to said Portland Cement Association Engineering Bulletin (Thickness Design for Concrete Highway and Street Pavements, Portland Cement Association, EB109P), the modulus of rupture (MR) of concrete should be estimated as the average 28-day flexural strength. The value of flexural strength multiplied by 50 psi, which is less than the experimental estimation of the mean value of this strength but is nearest to it, should be chosen as the modulus of rupture (MR) of this concrete.

It is well known that flexural strength is not an inherent quality of concrete as is compressive strength. Compressive strength of concrete is the best studied quality of concrete, and it is very important to provide means for estimation of statistical characteristics of flexural strength of concrete by means of those for compressive strength of this concrete. The statistical characteristics of flexural strength of normal concrete in connection with those for compressive strength of this concrete were obtained by processing the data of the results of American tests of cylindrical compressive strength and flexural strength of concrete, and American and British tests of the compressive strength of modified cubes and the flexural strength of concrete (Sapozhnikov N. Safety of Precast Reinforced Concrete and Prestressed Structural Members by the Second Limit State (Serviceability Limit State). State Committee of Construction of the USSR Institute of Information, Moscow, 1991, Table 6, FIG. 8). (See Appendix 3)

Statistical connections between compressive and flexural strength of concrete were estimated by the values of coefficient of correlation between these two types of concrete strength. Coefficients of correlation between the compressive and flexural concrete strength are equal to 0.831 and 0.865 for two big samplings of test results of 3650 standard cylinders and beams and 1107 modified cubes and standard beams, respectively. Connections between compressive and flexural concrete strength, which correspond to these values of coefficient of correlation, can be considered statistically significant. It allows the choice of modulus of rupture of concrete (MR) of concrete for thickness design of pavement depending on the specified compressive strength of this concrete.

Using the test results of 3,650 of standard cylinders and beams, the mean value of flexural strength of concrete fr can be estimated depending on the mean value of cylinder compressive strength fc as equal to 9.42

fc. This estimation of the mean value of flexural strength of concrete corresponds to the theoretical line of linear regression between compressive and flexural strength of concrete. It can be considered as legitimate at least in the range of the change of compressive strength from 2,500 to the 4,750 psi; as can be seen from the Fig.8, theoretical and empirical lines of regression in this range of change of compressive strength coincide completely. Since the deviation of empirical line of regression from theoretical one is small up to compressive strength of concrete equal to 6,000 psi, estimation of the mean value of flexural strength equal to 9.42

fc can be considered as legitimate in the range of change compressive strength from 2,500 to 6,000 psi.

Since the main estimation of compressive strength of concrete in American building practice is cylinder strength, the modified cube strength was assessed as cylinder by dividing by 1.2; the cubic strength of concrete is higher than that of cylindrical by 20% on average. Using the test results of 1107 of modified cubes and standard beams, the mean value of flexural strength of concrete fr can be estimated depending on the mean value of modified cubes compressive strength of this concrete fcu.mod is equal to 9.53

fcu.mod/1.2. Estimations of the mean value of the flexural strength of concrete obtained depending on the mean values of the compressive cylindrical and modified cubes strength of this concrete brought to cylindrical strength are very close and can be considered adequate.

According to said American building code ACI 318, the mean value of compressive strength of concrete fc considered as the required average strength fcr in terms of the ACI 318 must exceed the specified compressive strength fc′ by at least 1.34 s(fc), where s(fc) is the standard deviation of this strength. The values of the coefficient of variation for compressive and flexural strength of concrete are assumed usually as equal to 15% (Thickness Design for Concrete Highway and Street Pavements, Portland Cement Association, EB109P, p. 34). Based on value of coefficient of variation equal to 15%, this excess can be estimated as 25% of value of specified compressive strength fc′. Thus, the mean value of compressive strength of concrete fc can be considered as corresponding to certain value of specified compressive strength fc′. Due to close statistical connections between the compressive and flexural strength of concrete, mean value of flexural strength of this concrete fir estimated as 9.42

fc can also be considered as corresponding to this value of specified compressive strength.

The value of flexural strength multiplied by 50 psi, which is less than the estimation of the mean value of this strength but is nearest to it, should be chosen as the modulus of rupture (MR) of this concrete. Values of specified compressive strength fc′ equal to 3,000, 3,500, 4,000, 4,500 and 5,000 psi corresponds to the values of modulus of rupture (MR) equal to 550, 600, 650, 700, and 750 psi, respectively, coefficient of variation of compressive strength of concrete being assumed as 15%. These estimations of modulus of rupture of concrete are stable as to the change of coefficient of variation of compressive strength of concrete. concrete with all types of coarse aggregate of regular sizes. A considerable part of these aggregates relates to the hard rock (gravel, crushed gravel, and crushed granite). It is well known that flexural strength of concrete with this coarse aggregate is in the range from 10 to12 percent of compressive strength of concrete, and it increases up to the 15 percent of compressive strength for concrete with crushed limestone of regular sizes as a coarse aggregate.

It can be expected that the higher flexural strength of concrete with small grains crushed limestone as a coarse aggregate than that for concrete of the same consumption of cement with crushed limestone of regular sizes as a coarse aggregate. It is possible due to more complete penetration of mortar into small grains crushed limestone and more uniform structure of concrete with this coarse aggregate than that for concrete of crushed limestone of regular sizes as a coarse aggregate. The first flexural tests of concrete with crushed limestone as a coarse aggregate of grading intermediate between that for coarse and fine aggregate in the Terminology ASTM C125 confirm this tendency. In these tests the values of flexural strength of concrete equal to 418, 657 and 771 psi correspond to the values of compressive strength equal to 1,476, 2,821, and 4,166 psi, respectively. Flexural strength of concrete in these tests is in the range from 28.35 to 18.5 percents of compressive strength, diminishing with the increase of compressive strength. It does not mean the possibility of such estimations of modulus of rupture of concrete depend on the compressive strength of this concrete. There are only test results of the 3 series of two standard cubes brought to cylinder strength and two standard beams. However it means the tendency which should be checked during the mass production of concrete with crushed limestone of this grading for road construction.

An estimation of coefficient of variation of normal concrete strength equal to 15% is usually assumed and is incorporated into the design charts and tables of ACI and Portland Cement Association documents both for compressive and flexural strength. Concrete with enriched limestone waste as a coarse aggregate is more homogenous than concrete with crushed granite and crushed limestone of regular sizes as a coarse aggregate. The degree of uniformity of this concrete can be considered as intermediate between that for normal concrete with coarse aggregate of regular sizes and mortar. It means that the coefficient of variation of strength of concrete with the enriched limestone waste as coarse aggregate should be less than for concrete with coarse aggregate of regular sizes. Reduction of the coefficient of variation of compressive strength of concrete means the possibility to reduce compressive average strength required according to said American building code ACI 318 with a corresponding reduction of consumption of cement for this concrete.

Concrete with crushed limestone of grading intermediate between the least Size of coarse aggregates No.89 and the largest Size of fine aggregate No.9 according to ASTM C33 was checked in industrial conditions. Crushed limestone of this grading was used as a coarse aggregate for concrete of precast reinforced concrete temporary road slabs 1.75×3.0×0.16 m dimensions. More than 500 these slabs were produced on September-October 2002 at the Moscow plant referred above. These slabs are used for access roads to buildings under construction. They are placed usually into mud without any subbase and work separately. Conditions of service of these slabs under extensive truck traffic are more than adverse. However there are no financial claims to the plant connected with the strength of those slabs.

The use of concrete with this coarse aggregate allows very profitable utilization of great deposits of crushed limestone finer than 9.5 mm usually estimated as limestone quarry waste and especially aggregate finer than 4.75 mm. In so doing the volume of utilized aggregate finer than 4.75 mm as a raw material can be estimated as at least about 50% of the volume of utilized aggregate finer than 9.5 mm.

Operation of Still Additional Embodiment

The main aim of operation is to obtain concrete with enriched limestone waste as a coarse aggregate of grading optimal in terms of compressive and flexural strength of concrete. It means that in the aggregate bin of concrete plant the amount of aggregate finer than 4.75 mm should be about ⅔ of the total weight of aggregate, the amount of aggregate finer than 4.75 mm but coarser than 2.36 mm should be about 55-60% of the total weight of aggregate, the amount of aggregate finer than 0.3 mm should not exceed about 3% of the total weight of aggregate. Cost of aggregate fmer than 9.5 mm and coarser than 4.75 mm depends on the proportion between amounts of aggregate finer and coarser than 4.75 mm before enrichment; cost of aggregate finer than 4.75 mm is considerably less than that for aggregate coarser than 4.75 mm.

Amount of aggregate finer than 4.75 mm before enrichment should about 50% of the total weight of aggregate. It is determined depending on the breakdown of this aggregate due to handling and transportation to aggregate bin of concrete plant. Since more coarse parts of aggregate are more vulnerable due to scale effect, breakdown of aggregate relates mainly to its part coarser than 4.75 mm. Breakdown of aggregate depends on the its water-absorption, weather conditions, conditions of handling and transportation, and should be estimated experimentally. The breakdown of aggregate of ten-percent water-absorption under adverse weather conditions, adverse conditions of handling and transportation to aggregate bin of concrete plant results in doubling the increase of aggregate finer than 4.75 mm. The breakdown of aggregate of less water-absorption should be less, and proportions between amounts of aggregate of finer and coarser than 4.75 mm before enrichment and in aggregate bin of concrete plant should be closer. Moreover, the breakdown of aggregate coarser than 4.75 mm caused by screening as a dry enrichment of aggregate should be taken into account also.

Excessive breakdown of enriched limestone waste as a coarse aggregate causes a reduction of concrete strength, which should be compensated by additional consumption of cement. Grading of crushed limestone finer than that corresponding to the Size number 9 is considered as unacceptable for its utilization as a coarse aggregate since it requires an increase of consumption of cement non-proportional to the degradation of aggregate.

Stockpiled limestone fines is a washed and clean material. According to the invention amount of material finer than 0.3 mm should not exceed about 3% of the total weight of aggregate. Such requirements allow carrying out of enrichment of this material by inexpensive sizing without the more expensive washing.

Conclusion

Composite concrete pavement includes a surface course of concrete with hard rock coarse aggregate or asphalt, thickness of surface course being determined by requirements for abrasion resistance, and a subbase of specified compressive strength and modulus of rupture up to 5,000 psi and more than 750 psi, respectively. The coarse aggregate of subbase concrete defined as enriched limestone waste is a processed by-product of the manufacture of crushed limestone of regular sizes. Since this by-product is washed and clean material and the amount of grains finer than 0.3 mm is limited by about 3% of the total weight of aggregate, its enrichment can be carried out by inexpensive sizing without the more expensive washing.

According to the definition of ASTM C 125 (Standard Terminology Relating to Concrete and Concrete Aggregates) “coarse aggregate, n-(1) is aggregate predominantly retained on the 4.75-mm (No.4) sieve; or (2) that portion of an aggregate remained on the 4.75-mm (No.4) sieve”. As applied to the enriched limestone waste as a coarse aggregate of claimed concrete in aggregate bin of concrete plant the amount of aggregate finer than 4.75 mm (Sieve No.4) should be about ⅔ of the total weight of aggregate. The main part of this aggregate should be coarser than 2.36 mm; the amount of aggregate finer than 2.36 mm (Sieve No.8) should not exceed about 10% of the total weight of aggregate. The amount of aggregate finer than 1.18 mm (Sieve No.16) should not exceed about 7% of the total weight of aggregate. The amount of aggregate finer than 300 μm (Sieve No. 50) should not exceed about 3% of the total weight of aggregate. The grading of enriched limestone waste in the aggregate bin of a concrete plant should be finer than the least Size of coarse aggregate number 89 and coarser than for largest Size of fine aggregate number 9 according to ASTM C 33. This grading can be considered as intermediate between the coarse and fine aggregates in Terminology of ASTM C125. Moreover, this grading can be considered as optimal in terms of compressive and especially flexural strength of concrete, and in terms of utilization of great deposits of limestone finer than 4.75 mm.

Limestone quarry waste as a raw material for enrichment should be finer than 9.5 mm. The amount of aggregate finer than 4.75 mm (Sieve No.4) before enrichment should be about 50%. After enrichment the main part of aggregate finer than 4.75 mm should be coarser than 2.36 mm. The amount of aggregate finer than 2.36 mm (Sieve No. 8) after enrichment should not exceed about 10%; the amount of aggregate finer than 1.18 mm (Sieve No. 16) should not exceed about 7%; the amount of aggregate finer than 300 μm (Sieve No. 50) should not exceed about 2%.

Grading of this aggregate at the quarry after enrichment and in the aggregate bin of concrete plant differs due to inevitable breakdown of aggregate caused by handling and transportation from quarry to concrete plant. Due to scale effect large grains are more vulnerable, and breakdown of aggregate relates mainly to its part coarser than 4.75 mm. As a result, amount of aggregate finer than 4.75 mm after transportation to aggregate bin of concrete plant should be increased. The breakdown of aggregate should be estimated experimentally and taking into consideration when determining of proportion between parts of aggregate finer and coarser than 4.75 mm before enrichment of this aggregate.

The grading of coarse aggregate intermediate between the coarse and fine aggregates in Terminology of ASTM C125 can be considered as optimal in terms of concrete strength. Compressive strength of concrete with crushed limestone of this grading as a coarse aggregate is higher at least by 10% than that of concrete of the same consumption of cement with crushed limestone of grading corresponding to that of the Sizes 89 and 9. Moreover, compressive strength of concrete with crushed limestone of this grading as a coarse aggregate is substantially as high or higher than that of concrete of the same consumption of cement and twice as high consumption of admixture with crushed granite of regular sizes No. 57 and No. 67 of nominal dimensions 25.0 to 4.75 mm and 19 to 4.75 mm, respectively, as a coarse aggregate, while the flexural strength of this concrete is higher than that for concrete of the same consumption of cement with crushed granite of said Sizes No. 57 and No. 67 as a coarse aggregate, concrete with crushed granite of said regular sizes being considered as the standard in the world construction practice.

Variation of grading of enriched limestone waste is inevitable, and excessive degradation of this aggregate should be considered as possible. Excessive breakdown of aggregate does not mean impossibility of its use as a coarse aggregate for concrete. However it requires additional consumption of cement; grading of aggregate finer than corresponding to the Size number 9 is consider as unacceptable.

Close statistical connections between compressive and flexural strength of concrete allows estimation of modulus of rupture of concrete depending on the specified compressive strength of this concrete. It means the possibility to carry out mix design of road concrete based on the average compressive strength required according to ACI 318 and replacement of mix design according to the modulus of rupture of concrete by more convention design according to the value of the specified compressive strength of concrete corresponding to the value of modulus of rupture of this concrete.

Enriched limestone waste is one of the cheapest aggregates. However, the use of this aggregate allows obtaining concrete of specified compressive strength fc′ and modulus of rupture (MR) up to 5,000 and more than 750 psi, respectively. The area of application of concrete with this coarse aggregate and that of concrete with crushed limestone of regular sizes is the same. Using of this concrete for the subbase allows a considerable reduction of thickness of the normal concrete surface course; its thickness is determined by the requirements for abrasion resistance of a normal concrete surface. The use of concrete of a different cost but of the same compressive and flexural strength for different parts of a composite pavement allows one to obtain composite concrete pavement of the equivalent normal concrete thickness equal to the total thickness of subbase and concrete surface course.

The use of very inexpensive and efficient concrete with enriched limestone waste as a coarse aggregate for composite concrete pavement allows a reduction in the initial cost of construction of this pavement and makes this pavement more competitive as compared with asphalt pavement. Moreover, the use of concrete with this coarse aggregate allows very profitable utilization of great deposits of crushed limestone finer than 9.5 mm usually estimated as limestone quarry waste and especially aggregate finer than 4.75 mm. In so doing the volume of utilized aggregate finer than 4.75 mm should constitute at least ⅓ of the volume of utilized aggregate finer than 9.5 mm. Utilization of limestone waste make possible reduction of quarrying of high-quality aggregate with a corresponding conservation of environment.

Reduction of maintenance cost of pavement can be achieved by the replacement of a surface course of concrete with hard rock coarse aggregate by an asphalt surface course, thickness of the surface course in all cases being determined by the requirements for abrasion resistance. The existence of an asphalt surface course causes a reduction of the temperature stresses and mitigation of the effects of distress factors in the joints between slabs. 

1. A composite concrete pavement of highways, streets, and airfields comprising a surface course of thickness determined by requirements for abrasion resistance and a concrete subbase wherein the coarse aggregate of the concrete of said subbase is of small grains crushed limestone finer than 9.5 mm of grading intermediate between the least Size of coarse aggregate No.89 and largest Size No.9 of fine aggregate according to ASTM C33, the amount of material finer than 4.75 mm being about ⅔ of the total weight of said coarse aggregate.
 2. The composite concrete pavement of claim 1 wherein the coarse aggregate of the concrete of said subbase is defined as enriched limestone waste and is a by-product of the manufacture of limestone coarse aggregate of regular sizes.
 3. The composite concrete pavement of claim 1 wherein the concrete of said subbase is characterized by specified compressive strength fc′ and modulus of rupture up to 5,000 psi and more than 750 psi, respectively.
 4. The composite concrete pavement of claim 1 wherein said surface course is of concrete with hard rock as a coarse aggregate.
 5. The composite concrete pavement of claim 1 wherein said surface course is of asphalt.
 6. The composite concrete pavement of claim 1 wherein the amount the of coarse aggregate of the concrete of said subbase finer than finer than 2.36 mm corresponding to the Sieve No.8 according to ASTM C33 does not exceed about 10% of the total weight of said coarse aggregate.
 7. The composite concrete pavement of claim 1 wherein the amount of the coarse aggregate of the concrete of said subbase finer than finer than 1.18 mm corresponding to the Sieve No.16 according to ASTM C33 does not exceed about 7% of the total weight of said coarse aggregate.
 8. The composite concrete pavement of claim 1 wherein the amount the of coarse aggregate of the concrete of said subbase finer than finer than 0.3 mm corresponding to the Sieve No.50 according to ASTM C33 does not exceed about 3% of the total weight of said coarse aggregate.
 9. A composite concrete pavement of highways, streets, and airfields comprising a surface course of thickness determined by requirements for abrasion resistance and a concrete subbase of specified compressive strength fc′ and modulus of rupture up to 5,000 psi and more than 750 psi, respectively, with small grains crushed limestone finer than 9.5 mm of grading intermediate between the least Size of coarse aggregate No.89 and largest Size No.9 of fine aggregate according to ASTM C33 as a coarse aggregate wherein: said coarse aggregate of the concrete of said subbase defined as enriched limestone waste is a processed by-product of the manufacture of crushed limestone of regular sizes, the physical properties of this coarse aggregate are in accordance with requirements of ASTM C33; the amount of coarse aggregate of the concrete of said subbase finer than 4.75 mm is about two-thirds of the total weight of said coarse aggregate and less than that of the largest Size of fine aggregate number 9 according to ASTM C33; the amount of coarse aggregate of the concrete of said subbase finer than 2.36 mm corresponding to the Sieve No.8 according to ASTM C33 does not exceed about 10% of the total weight of said coarse aggregate; the amount of coarse aggregate of the concrete of said subbase finer than 1.18 mm corresponding to the Sieve No. 16 according to ASTM C33 does not exceed about 7% of the total weight of said coarse aggregate; the amount of coarse aggregate of the the concrete of said subbase finer than 300 μm corresponding to the Sieve No.50 according to ASTM C33 does not exceed about 3.0% of the total weight of said coarse aggregate; the share of cement per m³ of mix of said concrete being in the range of 175 to 500 kg; the share of water per m³ of said concrete mix being in the range of 140 to 225 kg; the share of sand as a fine aggregate per m³ of said concrete mix being in the range of 500 to 950 kg; the share of said coarse aggregate per m³ of said concrete mix being in the range of 1,080 to 1,150 kg;
 10. The composite concrete pavement of claim 9 wherein said surface course is concrete with crushed hard rock as a coarse aggregate, said concrete surface course being connected monolithically with the concrete of said subbase having a specified compressive strength fc′ up to 5,000 psi and modulus of rupture more than 750 psi, the coarse aggregate of said sabbase being defined as enriched limestone waste.
 11. The composite concrete pavement of claim 9 wherein said surface course is an asphalt cover layer of thickness determined by requirements for abrasion resistance, the capacity of said composite pavement being determined completely by the concrete of said subbase of specified compressive strength fc′ and modulus of rupture up to 5,000 psi and more than 750 psi, respectively, with said coarse aggregate defined as enriched limestone waste.
 12. The composite concrete pavement of claim 1 wherein the compressive strength of the concrete of said subbase is higher at least by 10% and than that of concrete of the same consumption of cement with crushed limestone as a coarse aggregate of grading corresponding to that of the least Size of coarse aggregate No.89 and largest Size No.9 of fine aggregate according to ASTM C33.
 13. The composite concrete pavement of claim 9 wherein the compressive strength of said concrete of said subbase is substantially as high or higher than that of concrete of the same consumption of cement and twice as high consumption of admixture with coarse aggregate of crushed granite of regular sizes No. 57 and No. 67 of nominal dimensions 25.0 to4.75 mm and 19 to 4.75 mm, respectively, while the flexural strength of said concrete is higher than that for concrete of the same consumption of cement with crushed granite of regular sizes as a coarse aggregate, concrete with crushed granite of said regular sizes being considered as the standard in the world construction practice.
 14. The composite concrete pavement of claim 9 wherein the mix design of the concrete of said subbase is determined by the value of modulus of rupture equal to the mean value of 28-day flexural strength of said concrete according to Portland Cement Association Engineering Bulletin EB 109P, said mean value of 28-day flexural strength of concrete being estimated as 9.42√ f_(cr)′ where f_(cr)′ is the mean value of 28-day compressive strength defined according to American building code ACI 318 as the required average 28-day compressive strength of said concrete,
 15. The composite concrete pavement of claim 14 wherein the required average 28-day compressive strength of the concrete of said subbase is determined depending on the value of specified compressive strength f_(c)′ of said concrete according to American building code ACI 318, the modulus of rupture of said concrete being equal to the mean value of flexural strength depending also on the value of specified compressive strength f_(c)′ of said concrete.
 16. The composite concrete pavement of claim 14 wherein mix design of said concrete of subbase determined by said value of modulus of rupture equal to the mean value of flexural strength of this concrete can be replaced by the more convenient mix design of said concrete of specified compressive strength fc′ corresponding to said value of modulus of rupture.
 17. The composite concrete pavement of claim 14 wherein mix design of the concrete of said subbase of values of modulus of rupture (MR) equal to 450, 500, 550, 600, 650, 700, and 750 psi can be carried out according to the values corresponding to the 28-day values of specified compressive strength fc′ equal to 2,000, 2,500, 3,000, 3,500, 4,000, 4,500 and 5,000 psi, respectively. 